(1) The interaction between the ground and the tunnel support is essential for the stability of the tunnel.(2) The subgrade reaction makes the bending moment of the tunnel lining arch small.(3) Even the thinner lining is able to supprt the surrounding ground if no buckling occurs.(4) The thicker lining is more likely to show the bending failure due to the bending moment.(5) Even if the concrete lining breaks due to the bending moment, the whole structure of lining can keep stability as long as the ground reaction is expected to some extent.These results were extracted by assuming a simple mechanical model of tunnelling without any consideration of the construction process. It is required to refine the above statements from the view points of more practical methods as well as the laboratory testing.